With their baseball hats and sauntering gaits, they appeared to friends and neighbors like ordinary American boys. But the Boston bombing suspects were refugees from another world — the blood, rubble and dirty wars of the Russian Caucasus.

Tamerlan Tsarnaev, 26, was a southpaw heavyweight boxer who represented New England in the National Golden Gloves and talked about competing on behalf of the United States. His tangle-haired 19-year-old brother, Dzhokhar, was a skateboarder who listened to rap and seemed easygoing to other kids in his Cambridge, Mass., neighborhood.

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MAP | Explore the sequence and locations of the unfolding events in the Boston area.

Tamerlan is now dead, killed in a shootout with police. Police said Friday night they had taken Dzhokhar into custody after he was cornered in a boat stored in a back yard in Watertown, Mass., after a massive manhunt. Hidden behind the lives they had been leading in Massachusetts is a biography containing old resentments that appear to have mutated into radical Islamic violence.

The brothers who are alleged to have planted bombs near the finish line of the Boston Marathon on Monday reached the United States in 2002 after their ethnic Chechen family fled the Caucasus. They had been living in the Central Asian republic of Kyrgyzstan and were prevented from resettling in war-racked Chechnya.

In speaking about his boxing career in 2009, Tamerlan told a photographer that in the absence of an independent Chechnya he would rather compete for the United States than for Russia, a hint that past troubles were not forgotten. He appeared increasingly drawn to radical Islam. On a YouTube channel, he recently shared videos of lectures from a radical Islamic cleric; in one, voices can be heard singing in Arabic as bombs explode.

“My son Tamerlan got involved in religious politics five years ago,” his mother, Zubeidat K. Tsarnaeva, told Russia Today television in an interview from Dagestan, the Russian republic bordering Chechnya where she and her husband live. “He started following his own religious aspects. He never, never told me he would be on the side of jihad.”

FBI officials confirmed Friday that they questioned Tamerlan in 2011 at the request of the Russian government about possible connections to Chechen extremists. He was interviewed by the FBI in Boston, and the investigation found “no derogatory information.”

His younger brother, who was widely known as “Jahar,” may have followed in his footsteps. “He talked about his brother in good ways,” said Pamala Rolon, who was the residential adviser in the dorm where Dzhokhar lived at the University of Massachusetts at Dartmouth. “I could tell he looked up to his brother.”

Although terrorists from the Caucasus have struck in Moscow and other parts of Russia, the conflict in the region has never led to attacks in other countries. One possible explanation for the Boston bombings, said Aslan Doukaev, an expert on the Caucasus who works for Radio Liberty in Prague, is that the brothers were motivated by radical jihadism, not Chechen separatism.

As the war in Chechnya wound down after Russian forces withdrew — they left formally in 2009 — violence has spilled into neighboring republics such as Dagestan, where the Tsarnaev family once found shelter and where the brothers’ parents now live. That conflict is increasingly marked by radical Islamic terrorism in an often vicious cycle of attack and reprisal between insurgents and Russian security forces. Tamerlan visited Dagestan last year, according to an official with knowledge of his travels.

Speaking to journalists in Dagestan on Friday, the brothers’ father, Anzor Tsarnaev, said his sons never had any interest in weapons. “I believe my children were set up,” he said.

Ramzan Kadyrov, the Chechen leader, said in a statement that attempts “to draw a parallel between Chechnya and the Tsarnaevs, if they are guilty, are futile. They grew up in the U.S., and their views and beliefs were formed there. The roots of the evil should be looked for in America.”

When the brothers were young, the family lived in Kyrgyzstan, a former republic of the Soviet Union in Central Asia, home to a small Chechen diaspora. Dzhokhar, the younger brother, was reportedly born there, although his older brother was born in Russia, according to some news reports.

The family lived in Tokmok, a town of about 55,000 people in northern Kyrgyzstan, near the border with Kazakhstan, the Kyrgyz National State Security Committee said in a statement Friday. Kyrgyz officials said the family left the country about 12 years ago for Dagestan, and after a year there immigrated to the United States.

Anzor Tsarnaev and his wife arrived in the United States in early 2002 after gaining refu­gee status. Their two sons and two daughters followed a short time later with an aunt.

The father worked as an auto mechanic. Jerry Siegel, owner of Webster’s Auto Body, in Somerville, Mass., said that the elder Tsarnaev worked for him for about 18 months and that he was an excellent mechanic who spoke very little English.

“He was just a hard-working, strong, tough guy,” Siegel said. “He would get under a car in the middle of winter, did whatever I asked.”

Siegel said Anzor left about four years ago for another mechanic’s job. Sometime after that, Anzor got sick and returned to Russia, according to other officials.

His wife is registered as a cosmetologist. If she returns to the United States, she is facing a criminal trial in Natick, Mass., after police said they arrested her last year trying to steal up to nine women’s dresses from a Lord & Taylor store at a local mall.

Tamerlan studied accounting at Bunker Hill Community College for three semesters as a part-time student between the fall of 2006 and the fall of 2008, according to Patricia Brady, a college spokeswoman.

When Tamerlan dropped out of school, his father was “desperate,” according to Anzor’s sister, Maret.

“The father had very high expectations for his son,” she said at a news conference in Toronto.

Tamerlan began boxing shortly after arriving in the United States. He registered with USA Boxing, the governing body for Olympic-style boxing, as early as 2003 and steadily rose through the ranks. By 2009, he reached the national Golden Gloves tournament in Salt Lake City, where he lost in a three-round decision bout with a boxer from Chicago.

Colleagues all described him as athletic and aggressive. “He was tall, taller than most of the guys, and tough,” said Paul Barry, vice president of the New England Boxing Association in Worcester, Mass., who once judged one of Tamerlan’s bouts.

Tamerlan was arrested in 2009 and charged with domestic assault and battery after allegedly assaulting his girlfriend, according to Spotcrime.com, an online source of crime information.

Tamerlan was married to Katherine Russell, 23, and the couple had a baby daughter, according to neighbors. They met while Katherine was studying at a college in Boston and recently spent considerable time at her childhood home in North Kingstown, R.I., according to neighbors.

Russell’s family gave a typewritten statement to reporters at their home Friday evening that read in part: “We cannot begin to comprehend how this horrible tragedy occurred. In the aftermath of the Patriot’s Day horror, we know that we never really knew Tamerlane [sic] Tsarnaev.” Her mother, Judith Russell, declined to comment further.

One next-door neighbor, Paula Gillettte, said Katherine had gone through a dramatic transition in her dress since going to college in Boston. When she returned for visits, she was wearing a head covering and the long-flowing gowns of traditional Muslim women; she also stayed inside more.

In 2011, Dzhokhar graduated high school, where he was the captain of the wrestling team, and went on to study at the University of Massachusetts. He hoped to become a dentist.

Dzhokhar was an avid skateboarder, and the night before the Monday bombings he cruised down Norfolk Street toward the house where his family has lived, said Caprice Ruff, 18, a grocery store cashier who lives about five houses away, across the street, on the same block in Cambridge.

She and family members were on their porch, and one called out a greeting and complimented him on his skateboard about 10:30 p.m., Ruff recalled. He answered something like, “Yeah, thanks,” she said.

Ruslan Tsarni, an uncle of the suspected bombers, said he is ashamed of them and earlier Friday urged Dzhokhar to turn himself in and beg forgiveness from the bombing victims. Asked what provoked his nephews, he replied: “Being losers — hatred to those who were able to settle themselves.”

“We are Muslim. We are ethnic Chechens,” he told reporters outside his house in Montgomery Village. “Somebody radicalized them, but it was not my brother. . . . Of course, we are ashamed. They are the children of my brother, who has little influence [over] them.”